In order to meet the requirements of C-IoT, a new access system for the Narrowband-Cellular Internet of Things (NB-IoT) was presented at the 69th plenary session of the 3rd Generation Partnership Project (3GPP); the research field pays particular attention to the low-complexity, low-throughput radio frequency (RF) technology of NB-IoT, with primary research aims comprising: improved indoor coverage, a high volume of low-throughput user equipment (UE) support, low latency sensitivity, extremely low equipment cost, low device power loss, and network architecture. The uplink and downlink transmission bandwidth for the NB-IoT system is 180 kHz, the same bandwidth as a physical resource block (PRB) in the Long-Term Evolution (LTE) system, which facilitates the reuse of design related to the existing LTE system. In addition, the NB-IoT system technology supports three different operating modes: 1) Stand-alone operation, such as the frequency spectrum used by GSM evolved radio access network systems with enhanced data rates (GERAN, GSM EDGE Radio Access Network) to replace one or multiple GSM carriers; 2) Guard band operation, such as the use of unused resource blocks (RB) within an LTE carrier guard band; 3) In-band operation, such as using an RB within the normal range of an LTE carrier.
Within the LTE system, the first system information broadcast (SIB1) message is used to carry necessary system information, wherein, SIB1 messages are transmitted in subframe 5 of every even-numbered radio frame, and related channel coding or rate matching processes rely on a single subframe (i.e., a PRB allocated to each SIB1 message in every 5th subframe). In the existing LTE system, a PRB that is allocated to SIB1 messages can dynamically regulate based on SIB1's transport block size (TBS), and thus can obtain the appropriate coding rate; as a result, channel coding or rate matching based on single subframes is possible.
But because the bandwidth of the NB-IoT system is only 180 kHz—only equal to the size of 1 PRB in the LTE system—the greatest number of PRB able to be allocated to NB-IoT SIB1 messages is 1. As a result, it is not possible to dynamically regulate the number of PRB allocated based on the TBS of the NB-IoT SIb1 message with existing SIB1 transmission methods within the LTE system. Under these circumstances, the transmission performance of NB-IoT SIB1 messages will be undoubtedly and severely limited when the TBS of the NB-IoT SIB1 message exceeds a certain threshold if it is still based on channel coding or rate matching of a single subframe.